Written by Mark Jones
Polyester resins are used in adhesives and fillers. Automotive filler is one example that’s used extensively. This can of resin comes with a small tube of activator. Mixing in a small amount of activator initiates the cure chemistry — leading to a hard polymer, which can be sanded with excellent adhesion to metal.
Formulations for stone construction, stone repair, and wood filler employ the same chemistry. Gel coats for marine and bath applications are typically polyesters that work well and offer UV resistance. In many cases, repairs with epoxies — not widely known for their UV stability — are covered with polyester resin topcoats.
Polyesters also find use in the fabrication of composite materials, like fiberglass. They’re employed extensively in the production of kitchen, bath, marine, and enclosure products. Polyesters are also sold as casting resins.
Polyester resins are typically formed from the free-radical polymerization of dibasic acids or anhydrides and diols. Depending on the end-use, there are other free-radical polymerizable monomers, such as styrene. The hardeners used are typically peroxides. When mixed, a free-radical chain reaction creates a polymer.
The resins cure quickly, generally within minutes. Several applications benefit from the fast cure capability, such as the installation of kitchen countertops. Sanding or painting can be done almost immediately after curing. The resulting polymer is strong, chemically resistant and, for the most part, environmentally stable. However, the bonds are not quite as resilient as other adhesives.
Extreme care must be taken when using polyester resins. Always read the safety data sheet and manufacturer’s instructions. Polyesters frequently contain volatile monomers that can damage the eyes, skin, and mucous membranes. They can also be irritants if inhaled and allergic reactions are not uncommon.
Hardeners are reactive and can lead to similar risks as polyesters, including damage to the eyes, skin, and mucous membranes. They also can cause allergic reactions in some people. The presence of solvents and volatile monomers further presents a fire hazard. Use with caution.